I've just finished AN INTEGRATED APPROACH TO INTERMEDIATE JAPANESE. I am looking for a book to do next with my japanese teacher. Which one do You find better - Authentic Japanese: Progressing from Intermediate to Advanced or the Tobira books?

If you've already done AIAIJ, then Tobira will be mostly review for you. Authentic Japanese is the next step after AIAIJ. So if you want to review with a different textbook, get Tobira. Otherwise, get Authentic Japanese.

(I realize this is an older topic, but figured my response might be helpful to others with the same question).

Are you sure Authentic Japanese would be the next step? I would think there's a significant gap between IAIJ and Authentic Japanese as the first is for beginning intermediate and Authentic Japanese is at the beginning advanced level. At least, that's my understanding.